Since both of the above aluminum member and copper member are excellent in electrical conductivity and thermal conductivity, they are widely used for electrical and electronic parts, heat radiation parts, and the like.
Here, the copper member is excellent particularly in heat conductivity and has properties of high mechanical strength and large deformation resistance. On the other hand, the aluminum member is slightly inferior to copper in electrical conductivity and thermal conductivity, but the aluminum member has properties such as lightweight and a low deformation resistance.
Accordingly, in the electrical and electronic parts, heat radiation parts, and the like, depending on the required performance, the copper member and aluminum member are selectively used. Recently, from the viewpoint of size and weight of the electrical and electronic parts and heat radiation parts described above, there is a need for a bonding body in which the copper member and the aluminum member are bonded together.
Aluminum and copper, as shown in a phase diagram of FIG. 1, is known to produce various forms of intermetallic compounds, and when an aluminum member and a copper member are directly welded, these intermetallic compounds are produced in large amount and randomly in the bonding interface between the aluminum member and the copper member. Since these intermetallic compounds are very brittle compared to the copper member and aluminum member, the bonding interface between the copper member and the aluminum member becomes brittle locally, and bonding reliability between the copper member and the aluminum member could not be sufficiently secured.
As a method of bonding an aluminum member and a copper member, a friction welding method, a diffusion bonding method and the like, have been proposed. Also, for example, in Patent Documents 1 to 3, a method of bonding an aluminum member and a copper member together while suppressing the generation of intermetallic compounds has been proposed.
Diffusion bonding method is a method in which a heat treatment is carried out at a temperature of a melting temperature or lower after bonding the copper member and the aluminum member together in advance by drawing or pack rolling the copper member and the aluminum member.
In addition, a friction welding method is a method in which while the copper member and the aluminum member are pressed to each other, a friction of the copper member with the aluminum member is performed and they are bonding by the frictional heat and pressure.
Patent Document 1 discloses that a rod shaped aluminum member is inserted inside a tube shaped copper member, and then, a clad material in which the copper member and the aluminum member are bonded with a metallic bond is produced by performing drawing machining.
Patent Document 2 discloses that an insert material made of pure aluminum or the like is bonded to a copper member by cold rolling, an aluminum member is bonded to the insert material by hot rolling or cold rolling, and a heat treatment is carried out after the insert material is bonded to the copper member.
Furthermore, Patent Document 3 proposes a method in which a metal layer made of Ag is formed on a bonding surface of a copper member, and the metal layer and an aluminum layer are brazed.